1. Field of the Invention
The present invention generally relates to semiconductor devices and methods of making the semiconductor devices, and particularly relates to a semiconductor device and a method of making the semiconductor device in which the efficiency of heat dissipation regarding heat generated by a semiconductor chip is improved.
2. Description of the Related Art
In recent years, the circuit integration of semiconductor chips has been further enhanced, and there has been a demand for higher density for the implementation of semiconductor devices. Against this background, BGA-type semiconductor devices and LGA-type semiconductor devices, which achieve shorter pitches for external connection terminals (bumps, lands, etc.) compared with QFP (quad flat package)-type semiconductor devices, have been attracting attention, and have been put to practical use.
Moreover, the heat radiation of semiconductor devices increases as the circuit integration of semiconductor chips are further enhanced, resulting in a need to improve heat dissipation characteristics of semiconductor devices.
Various related-art semiconductor devices have been proposed that shorten the pitches of external connection terminals and improve heat dissipation characteristics (for example, Patent Document 1-4). FIG. 1 is an illustrative drawing showing an example of a related-art semiconductor device which is aimed at improving heat dissipation characteristics. A semiconductor device 1 shown in FIG. 1 has an FC-BGA (flip-chip bump grid-array package) structure, and schematically includes a semiconductor chip 2, a package substrate 3, a heat dissipation member 4, and solder balls 5.
The semiconductor chip 2 is mounted through flip-chip implementation on the upper surface of the package substrate 3. The solder balls 5 serving as external connection terminals are provided on the lower surface of the package substrate 3. The package substrate 3 is a multi-layered substrate, and the semiconductor chip 2 and the solder balls 5 are electrically coupled through internal wiring.
The heat dissipation member 4 serves as a lid that protects the semiconductor chip 2, and also serves as a heat dissipation plate that dissipates heat generated by the semiconductor chip 2. Because of this, the semiconductor chip 2 and the heat dissipation member 4 need to be thermally coupled. In the related art, a thermal coupling member 6 (hereinafter simply referred to as a coupling member) is used to provide thermal coupling between the back surface of the semiconductor chip 2 and the interior surface of the heat dissipation member 4.
In such a structure, two schemes as described in the following are typically employed as a heat conduction mechanism that conducts heat from the back surface of the semiconductor chip 2 to the heat dissipation member 4.
One of the schemes (scheme (a)) is to use a heat conductor such as grease (compound) or a heat conductive adhesive that has stress relaxation characteristics, and provide such heat conductor as the coupling member 6 between the semiconductor chip 2 and the heat dissipation member 4 in order to prevent the lowering of reliability that is caused by a mismatch of the coefficient of thermal expansion resulting from the differences of materials between the semiconductor chip 2 and the heat dissipation member 4. The other scheme (scheme (b)) is to provide a material (e.g., a composite material of Cu—W, carbon, and aluminum, etc.) having the coefficient of thermal expansion close to that of the semiconductor chip 2, thereby connecting between the semiconductor chip 2 and the heat dissipation member 4 through soldering.                [Patent Document 1]        Japanese Patent Publication No. 57-176750        [Patent Document 2]        Japanese Patent Publication No. 01-117049        [Patent Document 3]        Japanese Patent Publication No. 10-050770        [Patent Document 4]        Japanese Patent Publication No. 11-067998        
In the scheme (a) described above, either grease (compound) or a heat conductive adhesive has high thermal resistance, giving rise to a problem in that thermal conduction from the semiconductor chip 2 to the heat dissipation member 4 is not efficiently carried out. In the scheme (b) described above, the composite material of Cu—W, carbon, and Al or the like is used as a material having the coefficient of thermal expansion close to that of the semiconductor chip 2. Such material has relatively low thermal conductivity, compared with Cu or the like that has satisfactory heat dissipation characteristics. Because of this, the scheme (b) can only be used for a package in which heat generation by the semiconductor chip 2 is relatively low.
Accordingly, there is a need for a semiconductor device and a method of making the semiconductor device wherein heat generated by the semiconductor device is reliably dissipated, and, also, stress generated inside the device is reduced.